This invention relates to a process for the production of potassium titanate long fibers.
It has hitherto been known to produce fibrous potassium titanate by the so-called hydrothermal process in which a mixture of a tetravalent titanium compound and potassium compound is reacted in an aqueous alkaline solution at a high temperature and pressure in a pressure vessel. However, the hydrothermal reaction technique of the prior art has disadvantages in that it not only requires a considerably high temperature, high pressure and long reaction time, for example, at least 400.degree. C, 200 atmospheres (often 3000 atmospheres) and 70 hours, but also the formation of the fiber is stopped after a certain period of time. This is because, in spite of the above, the prior art process requires a concentrated alkaline solution to form good fibers. The alkaline concentration is gradually lowered by water formed during the reaction according to the following equation: EQU 6TiO.sub.2 nH.sub.2 O + 2KOH = K.sub.2 Ti.sub.6 O.sub.13 + (n + 1)H.sub.2 O (1)
the inventors have already proposed an improved hydrothermal process to overcome these disadvantages, in which the hydrothermal reaction is carried out with the removal of water present in the reaction system or formed during the reaction by using a metal having a larger ionization tendency than hydrogen or by a physical dehydrating method (Japanese patent application No. 114364/1973).
In the case of using such a metal in this prior invention, the metal (Me) is gradually oxidized by the following reaction: EQU Me + nH.sub.2 O = MeO.sub.n + nH.sub.2 ( 2)
and the dehydration is thus completed. A similar result can also be obtained by a physical dehydration, for example, removing gradually water by a valve from a pressure vessel instead of using such a chemical dehydrating agent. The physical dehydration is preferably carried out in such a manner that the content of water in the reaction system is decreased at a rate of about 0.2 to 5 % by weight per hour and finally reaches about 5 to 15 % by weight.
The inventors have made successive studies on the above mentioned pressure dehydration method and have found that the production of fibrous potassium titanate according to the pressure dehydration method can be carried out with a further improved yield by using, in addition to a tetravalent titanium compound, a lower valency titanium compound and/or metallic titanium as a raw titanium material. The present invention is based on this finding. This is possibly due to the fact that a lower valency titanium compound or metallic titanium is dissolved in pressurized water and subjected to oxidation reaction to form an activated tetravalent titanium compound which can promote the formation reaction and crystallization of fibrous potassium titanate.